10. Why is normal eye not able to see clearly the objects placed closer than 25 cm?

Ans:

This is because the focal length of eye lens can’t be decreased below a certain minimum limit (25 cm).

11. What happens to the image distance in the eye when we increase the distance of an object from the eye?

Ans:

For a normal eye, the image distance in the eye is fixed i.e., the distance of retina from the eye lens. When we increase the distance of the object from the eye, the focal length of eye lens is changed on account of accomodating power of eye so as to keep the image distance constant.

12. Why does it take some time to see the objects in a cinema hall when we just enter the hall?

Ans:

This is because the pupil of the eye takes some time to expand and allow more light to entre the eye.